86 THE MEIOTIC PHASE [CH. 



fore be concluded that the daughter-nuclei may contain 

 any combination of paternal and maternal chromosomes, 

 as long as one and one only of each kind is represented; 

 that is to say, any combinations such as A, B, C, . . . , A, 

 B', C, . . . , A', B, C', . . . are possible, but every letter must 

 be represented once and once only. In other words, it 

 appears that the function of the reducing division is 

 to ensure that each germ-cell shall contain one complete 



*&*% .::!:? 





- 



3 4 







567 



FIG. ii. Chromosomes of Biston hirtartus and Nyssia zonaria and 

 the hybrid between them, from HARRISON and DONCASTER. 



1,2. 2?. birtarius, spermatogonial group (i ) and first spermatocyte group (2). 

 3, 4. N.xonaria spermatogonial group (3) and first spermatocyte group (4). 

 5, 6, 7. Hybrid zonaria J and hirtarius $ : 5, spermatogonial group; 

 6, 7, first spermatocyte groups. 



haploid set, but that within this set all possible combina- 

 tions of chromosomes of paternal and maternal origin are 

 possible. 



That the bivalent chromosomes of the meiotic phase do 

 in fact consist of pairs, one of which is of paternal and the 

 other of maternal origin, is clearly shown by the behaviour 

 of the chromosomes in certain hybrids, especially in Moths, 

 and also in various plants. A particularly clear example is 

 seen in the hybrid between the moths Biston birtarius and 



